Natura - nature
   actualia - actual entities
     Mundus Plinius - physical world
       naturalia - natural bodies
         "crystal-kingdom"
           chemical substances
             reactive intermediates
               Class diradicals [X:, X•Y•]
                 01 Class boranylidenes [RB:]
                 02.1 Class carbenes [X2C:, X=C:]
                 02.2 Class fulminates [RON=C:]
                 03 Class nitrenes [RN:]
                 04 Class silylenes [R2Si:]
                 05 Class phosphanylidenes [RP:]
                 06 Class germylidenes [R2Ge:]
                 07 Class arsanylidenes [RAs:]
                 08 Class stannylidenes [R2Sn:]
                 09 Class stibanylidenes [RSb:]
                 10 Class plumbylidenes [R2Pb:]